Processability of silica-filled rubber stocks with reduced hysteresis

ABSTRACT

A silica-filled, vulcanized elastomeric compound comprises 100 parts by weight of an elastomer; from about 5 to about 100 parts by weight of a reinforcing filler per 100 parts of elastomer, wherein the reinforcing fillers are selected from the group consisting of carbon black and silica filler; from 0 to about 20 percent by weight of a silane, based upon the weight of the silica filler; a cure agent; from about 0 to about 20 parts by weight of a processing aid selected from the group consisting of fatty acid esters of hydrogenated and non-hydrogenated C 5  and C 6  sugars; from about 0 to about 20 parts by weight of a processing aid selected from the group consisting of polyoxyethylene derivatives of fatty acid esters of hydrogenated and non-hydrogenated C 5  and C 6  sugars; from about 0 to about 40 parts by weight of an additional filler other than silica or carbon black, with the provisos that at least one of the processing aids or additional fillers are present; that if the processing aid is sorbitan monooleate, then at least one of the polyoxyethylene derivatives or additional fillers is also present and, that the minimal amount for each processing aid and additional filler, if present, is about one part by weight. A process for the preparation of silica filled vulcanizable elastomers is provided as well as pneumatic tires employing tread stock comprising the novel vulcanizable elastomers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. Ser. No. 08/893,875,filed Jul. 11, 1997 now U.S. Pat. No. 6,369,138.

TECHNICAL FIELD

The subject invention relates to the processing and vulcanization ofdiene polymer and copolymer elastomer-containing rubber stocks. Morespecifically, the present invention relates to the processing andvulcanization of diene polymer and copolymer elastomer-containing,silica-filled rubber stocks using a fatty acid ester of hydrogenated andnon-hydrogenated sugars as a processing aid.

In another embodiment, the present invention relates to the processingand vulcanization of diene polymer and copolymer elastomer-containing,silica-filled rubber stocks containing additional mineral fillers.

BACKGROUND OF THE INVENTION

In the art it is desirable to produce elastomeric compounds exhibitingreduced hysteresis when properly compounded with other ingredients suchas reinforcing agents, followed by vulcanization. Such elastomers, whencompounded, fabricated and vulcanized into components for constructingarticles such as tires, power belts, and the like, will manifestproperties of increased rebound, decreased rolling resistance and lessheat-build up when subjected to mechanical stress during normal use.

The hysteresis of an elastomer refers to the difference between theenergy applied to deform an article made from the elastomer and theenergy released as the elastomer returns to its initial, undeformedstate. In pneumatic tires, lowered hysteresis properties are associatedwith reduced rolling resistance and heat build-up during operation ofthe tire. These properties, in turn, result in lower fuel consumptionfor vehicles using such tires.

In such contexts, the property of lowered hysteresis of compounded,vulcanizable elastomer compositions is particularly significant.Examples of such compounded elastomer systems are known to the art andare comprised of at least one elastomer (that is, a natural or syntheticpolymer exhibiting elastomeric properties, such as a rubber), areinforcing filler agent (such as finely divided carbon black, thermalblack, or mineral fillers such as clay and the like) and a vulcanizingsystem such as sulfur-containing vulcanizing (that is, curing) system.

Previous attempts at preparing readily processable, vulcanizable,silica-filled rubber stocks containing natural rubber or diene polymerand copolymer elastomers have focused upon the sequence of addingingredients during mixing (Bomal, et al., Influence of Mixing procedureson the Properties of a Silica Reinforced Agricultural Tire Tread, May1992), the addition of de-agglomeration agents such as zinc methacrylateand zinc octoate, or SBR-silica coupling agents such as mercapto propyltrimethoxy silane (Hewitt, Processing Technology of Silica ReinforcedSBR, Elastomerics, pp 33-37, March 1981), and the use ofbis[3-(triethoxysilyl) propyl]tetrasulfide (Si69) processing aid(Degussa, PPG).

The use of Si69 processing aid in the formulation of silica-filledrubber stocks has been successful, but generally requires a large amountof the additive, such as 10% by weight based on the weight of silica, inorder to be effective.

Precipitated silica has been increasingly used as a reinforcingparticulate filler in carbon black-filled rubber components of tires andmechanical goods. Silica-loaded rubber stocks, however, exhibitrelatively poor processability.

The present invention provides a fatty acid ester of hydrogenated andnon-hydrogenated sugars for use as a processing aid for silica-filledrubber stocks, which greatly improves the processability and propertiesof the formulations and the resulting vulcanized product. In anotherembodiment, the present invention further provides additional mineralfillers for use in silica-filled elastomeric rubber stocks, improvingtear strength and lowering hysteresis.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide processingaids which improve the processability of formulations of diene polymerelastomers reinforced with silica-filler.

It is another object of the present invention to provide mineral andnon-mineral fillers which improve the processability of formulations ofdiene polymer elastomers reinforced with silica-filler.

It is another object of the present invention to provide formulations ofdiene polymer elastomers reinforced with silica-filler having improvedprocessability with decreased levels silanes.

It is yet another object of the present invention to provide a processfor improving the processability of formulations of diene polymerelastomers reinforced with silica-filler.

It is another object of the present invention to provide a process forreducing the viscosity of silica-filled elastomeric vulcanizablecompounds.

It is still another object of the present invention to provide a processfor decreasing the level of silanes in silica-filled elastomericvulcanizable compounds.

It is another object of the present invention to provide vulcanizablesilica-filled elastomeric compounds having enhanced physical properties,including decreased hysteresis and increased tear strength.

At least one or more of the foregoing objects, together with theadvantages thereof over the existing art, which shall become apparentfrom the specification which follows, are accomplished by the inventionas hereinafter described and claimed.

The present invention provides a process for the preparation of asilica-filled, vulcanized elastomeric compound comprising mixing anelastomer with from about 5 to about 100 parts by weight of areinforcing filler per 100 parts of elastomer, wherein the reinforcingfillers are selected from the group consisting of carbon black andsilica filler; from 0 to about 20 percent by weight of a silane, basedupon the weight of the silica filler; a cure agent; from about 0 toabout 20 parts by weight of a processing aid selected from the groupconsisting of fatty acid esters of hydrogenated and non-hydrogenated C₅and C₆ sugars; from about 0 to about 20 parts by weight of a processingaid selected from the group consisting of polyoxyethylene derivatives offatty acid esters of hydrogenated and non-hydrogenated C₅ and C₆ sugars;from about 0 to about 40 parts by weight of an additional filler otherthan silica or carbon black, with the provisos that at least one of theprocessing aids or additional fillers are present; that if theprocessing aid is sorbitan monooleate, then at least one of thepolyoxyethylene derivatives or additional fillers is also present and,that the minimal amount for each processing aid and additional filler,if present, is about one part by weight; and, effecting vulcanization.

The present invention further provides a vulcanizable silica-filledcompound comprising 100 parts by weight of an elastomer; from about 5 toabout 100 parts by weight of a reinforcing filler per 100 parts ofelastomer, wherein the reinforcing fillers are selected from the groupconsisting of carbon black and silica filler; from 0 to about 20 percentby weight of a silane, based upon the weight of the silica filler; acure agent; from about 0 to about 20 parts by weight of a processing aidselected from the group consisting of fatty acid esters of hydrogenatedand non-hydrogenated C₅ and C₆ sugars; from about 0 to about 20 parts byweight of a processing aid selected from the group consisting ofpolyoxyethylene derivatives of fatty acid esters of hydrogenated andnon-hydrogenated C₅ and C₆ sugars; from about 0 to about 40 parts byweight of an additional filler other than silica or carbon black, withthe provisos that at least one of the processing aids or additionalfillers are present; that if the processing aid is sorbitan monooleate,then at least one of the polyoxyethylene derivatives or additionalfillers is also present and, that the minimal amount for each processingaid and additional filler, if present, is about one part by weight.

The present invention further provides a pneumatic tire employing treadstock manufactured from the vulcanizable silica-filled compound of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWING

The drawing FIGURE is a graph of Beta, an inverse measure of fillerassociation or crosslink density, as a function of mix energy.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the present invention, the polymerized elastomer, e.g.,polybutadiene, polyisoprene and the like, and copolymers thereof withmonovinyl aromatics such as styrene, alpha methyl styrene and the like,or trienes such as myrcene, is compounded to form the rubber stock.Thus, the elastomers include diene homopolymers, A, and copolymersthereof with monovinyl aromatic polymers, B. Exemplary dienehomopolymers are those prepared from diolefin monomers having from 4 toabout 12 carbon atoms. Exemplary vinyl aromatic polymers are thoseprepared from monomers having from 8 to about 20 carbon atoms. Examplesof conjugated diene monomers and the like useful in the presentinvention include 1,3-butadiene, isoprene, 1,3-pentadiene,2,3-dimethyl-1,3-butadiene and 1,3-hexadiene, and aromatic vinylmonomers include styrene, α-methylstyrene, p-methylstyrene,vinyltoluenes and vinylnaphthalenes. The conjugated diene monomer andaromatic vinyl monomer are normally used at the weight ratios of about90:10 to about 55:45, preferably about 80:20 to about 65:35.

Preferred elastomers include diene homopolymers such as polybutadieneand polyisoprene and copolymers such as styrene butadiene rubber (SBR).Copolymers can comprise from about 99 to 55 percent by weight of dieneunits and from about 1 to about 45 percent by weight of monovinylaromatic or triene units, totaling 100 percent. The polymers andcopolymers of the present invention may have 1,2-microstructure contentsranging from about 10 to about 80 percent, with the preferred polymersor copolymers having 1,2-microstructure contents of from about 25 to 65percent, based upon the diene content. The molecular weight of thepolymer that is produced according to the present invention, ispreferably such that a proton-quenched sample will exhibit a gum Mooneyviscosity (ML₄/212° F.) of from about 2 to about 150. The copolymers arepreferably random copolymers which result from simultaneouscopolymerization of the monomers, as is known in the art. Also includedare non-functionalized cis-polybutadiene, ethylene-propylene-dienemonomer (EPDM), emulsion styrene butadiene rubber, and natural rubber.

Initiators known in the art such as an organolithium initiator,preferably an alkyllithium initiator, can be employed to prepare theelastomer. More particularly, the initiators used in the presentinvention include N-lithio-hexamethyleneimine, organolithium compoundssuch as n-butyllithium, tributyltin lithium, dialkylaminolithiumcompounds such as dimethylaminolithium, diethylaminolithium,dipropylaminolithium, dibutylaminolithium and the like,dialkylaminoalkyllithium compounds such as diethylaminopropyllithium andthe like, and trialkyl stanyl lithium, wherein the alkyl group contains1 to about 12 carbon atoms, preferably 1 to about 4 carbon atoms.

Polymerization is usually conducted in a conventional solvent foranionic polymerizations such as the various cyclic and acyclic hexanes,heptanes, octanes, pentanes, their alkylated derivatives, and mixturesthereof. Other techniques for polymerization, such as semi-batch andcontinuous polymerization may be employed. In order to promoterandomization in copolymerization and to increase vinyl content, acoordinator may optionally be added to the polymerization ingredients.Amounts range between 0 to 90 or more equivalents per equivalent oflithium. The amount depends upon the amount of vinyl desired, the levelof styrene employed and the temperature of the polymerizations, as wellas the nature of the specific polar coordinator employed.

Compounds useful as coordinators are organic and include those having anoxygen or nitrogen hetero-atom and a non-bonded pair of electrons.Examples include dialkyl ethers of mono and oligo alkylene glycols;“crown” ethers; tertiary amines such as tetramethylethylene diamine(TMEDA); THF; THF oligomers; linear and cyclic oligomeric oxolanylalkanes, such as 2-2′-di(tetrahydrofuryl) propane, di-piperidyl ethane,hexamethylphosphoramide, N-N′-dimethylpiperazine, diazabicyclooctane,diethyl ether, tributylamine and the like. Details of linear and cyclicoligomeric oxolanyl coordinators can be found in U.S. Pat. No.4,429,091, owned by the Assignee of record, the subject matter of whichis incorporated herein by reference.

Polymerization is usually begun by charging a blend of the monomer(s)and solvent to a suitable reaction vessel, followed by the addition ofthe coordinator and the initiator solution previously described.Alternatively, the monomer and coordinator can be added to theinitiator. The procedure is carried out under anhydrous, anaerobicconditions. The reactants are heated to a temperature of from about 10°C. to about 150° C. and are agitated for about 0.1 to about 24 hours.After polymerization is complete, the product is removed from the heatand terminated in one or more ways. To terminate the polymerization, aterminating agent, coupling agent or linking agent may be employed, allof these It is to be understood that practice of the present inventionis not limited solely to these terminators inasmuch as other compoundsthat are reactive with the polymer bound lithium moiety can be selectedto provide a desired functional group.

Quenching is usually conducted by stirring the polymer and quenchingagent for about 0.05 to about 2 hours at temperatures of from about 30°to 150° C. to ensure complete reaction. Polymers terminated with afunctional group as discussed hereinabove, are subsequently quenchedwith alcohol or other quenching agent as described hereinabove.

Lastly, the solvent is removed from the polymer by conventionaltechniques such as drum drying, extruder drying, vacuum drying or thelike, which may be combined with coagulation with water, alcohol orsteam, thermal desolventization, or any other suitable method. Ifcoagulation with water or steam is used, oven drying may be desirable.

The elastomeric polymers can be utilized as 100 parts of the rubber inthe treadstock compound or, they can be blended with any conventionallyemployed treadstock rubber which includes natural rubber, syntheticrubber and blends thereof. Such rubbers are well known to those skilledin the art and include synthetic polyisoprene rubber, styrene/butadienerubber (SBR), including emulsion SBR's, polybutadiene, butyl rubber,neoprene, ethylene/propylene rubber, ethylene/propylene/diene rubber(EPDM), acrylonitrile/butadiene rubber (NBR), silicone rubber, thefluoroelastomers, ethylene acrylic rubber, ethylene vinyl acetatecopolymer (EVA), epichlorohydrin rubbers, chlorinated polyethylenerubbers, chlorosulfonated polyethylene rubbers, hydrogenated nitrilerubber, tetrafluoroethylene/propylene rubber and the like. When thefunctionalized polymers are blended with conventional rubbers, theamounts can vary widely within a range comprising about 5 to about 99percent by weight of the total rubber, with the conventional rubber orrubbers making up the balance of the total rubber (100 parts). It is tobe appreciated that the minimum amount will depend primarily upon thedegree of reduced hysteresis that is desired.

According to the present invention, amorphous silica (silicon dioxide)is utilized as a filler for the diene polymer or copolymerelastomer-containing vulcanizable compound. Silicas are generallyclassed as wet-process, hydrated silicas because they are produced by achemical reaction in water, from which they are precipitated asultrafine, spherical particles.

These primary particles strongly associate into aggregates, which inturn combine less strongly into agglomerates. The surface area, asmeasured by the BET method gives the best measure of the reinforcingcharacter of different silicas. For silicas of interest for the presentinvention, the surface area should be about 32 to about 400 m²/g, withthe range of about 100 to about 250 m²/g being preferred, and the rangeof about 150 to about 220 m²/g being most preferred. The pH of thesilica filler is generally about 5.5 to about 7 or slightly over,preferably about 5.5 to about 6.8.

Silica can be employed in the amount of about 1 part to about 100 partsby weight per 100 parts of polymer (phr), preferably in an amount fromabout 5 to about 80 phr. The useful upper range is limited by the highviscosity imparted by fillers of this type. Some of the commerciallyavailable silicas which may be used include: Hi-Sil® 215, Hi-Sil® 233,and Hi-Sil® 190, produced by PPG Industries. Also, a number of usefulcommercial grades of different silicas are available from De GussaCorporation, Rhone Poulenc, and J. M. Huber Corporation.

Although the vulcanizable elastomeric compounds of the present inventionare primarily silica-filled, the polymers can be optionally compoundedwith all forms of carbon black in amounts ranging from 0 to about 50parts by weight, per 100 parts of rubber (phr), with about 5 to about 40phr being preferred. When carbon is present, with silica, the amount ofsilica can be decreased to as low as about one phr, otherwise it too ispresent alone in at least 5 phr. As is known to those skilled in theart, elastomeric compounds as are discussed herein are typically filledto a volume fraction of about 25 percent which is the total volume offiller(s) added divided by the total volume of the elastomeric stock.Accordingly, while the minimum amounts expressed herein are operable, auseful range of reinforcing fillers i.e., silica and carbon black, isabout 30 to 100 phr.

The carbon blacks may include any of the commonly available,commercially-produced carbon blacks but those having a surface area(EMSA) of at least 20 m²/gram and more preferably at least 35 m²/gram upto 200 m²/gram or higher are preferred. Surface area values used in thisapplication are those determined by ASTM test D-1765 using thecetyltrimethyl-ammonium bromide (CTAB) technique. Among the usefulcarbon blacks are furnace black, channel blacks and lamp blacks. Morespecifically, examples of the carbon blacks include super abrasionfurnace (SAF) blacks, high abrasion furnace (HAF) blacks, fast extrusionfurnace (FEF) blacks, fine furnace (FF) blacks, intermediate superabrasion furnace (ISAF) blacks, semi-reinforcing furnace (SRF) blacks,medium processing channel blacks, hard processing channel blacks andconducting channel blacks. Other carbon blacks which may be utilizedinclude acetylene blacks. Mixtures of two or more of the above blackscan be used in preparing the carbon black products of the invention.Typical values for surface areas of usable carbon blacks are summarizedin TABLE I hereinbelow.

TABLE I Carbon Blacks ASTM Designation Surface Area (m²/g) (D-1765-82a)(D-3765) N-110 126 N-220 111 N-339 95 N-330 83 N-351 74 N-550 42 N-66035

The carbon blacks utilized in the preparation of the rubber compounds ofthe invention may be in pelletized form or an unpelletized flocculentmass. Preferably, for more uniform mixing, unpelletized carbon black ispreferred.

Recognizing that carbon black may be used as an additional reinforcingfiller with silica, the total amount of reinforcing filler(s) in thevulcanizable elastomeric compounds of the present invention rangesbetween about 30 to 100 phr, all of which can comprise silica or,mixtures with carbon black within the foregoing ranges. It is to beappreciated that as the amount of silica decreases, lower amounts of theprocessing aids of the present invention, plus silane, if any, can beemployed.

When silica is employed as a reinforcing filler, it is customary to adda silane e.g., bis[3-(triethoxysilyl)propyl]tetrasulfide, to obtain goodphysical properties in a cured rubber stock containing silica as afiller. In general, the present invention provides a means to reduce oreliminate the level of silane. This material is commonly added to silicafilled rubber formulations and will be referred to throughout thisspecification by its industry recognized designation, Si69, or simply asa silane. In addition, the present invention further providesmaintenance of the processability of the compounded stock, as measuredby Mooney viscosity, at the same level as achieved with high levels ofsilane. This replacement of the silane results in reduced cost andprovides a material that is stable for storage and is easily added torubber compounds. In addition, the use of vulcanizable elastomericcompounds according to the present invention provides the same or betterphysical properties upon curing. Generally, the amount of silane that isadded ranges between about 4 and 20 percent by weight, based upon theweight of silica filler present in the elastomeric compound. By practiceof the present invention, it is possible to reduce the amount of silanedown to about 5 percent, more preferably, 3 to 1 percent and mostpreferably, to eliminate its presence totally i.e., 0 percent. It mayalso be desirable to increase processability of the silica filledelastomer compounds without any decrease in silane content which can beaccomplished by the addition of a processing aid or filler according tothe present invention as is described hereinafter.

The present invention utilizes the presence of one or more processingaids to replace the silane (Si69) to give equal processability of thevulcanizable compound, and better hot tear strength and lower hysteresisof the vulcanized rubber stock, without loss of the other measuredphysical properties. The processing aids are air stable and do notdecompose. They are lower in cost and more storage stable than thesilane, and when used with silica filled elastomers, give similarreduction of ML₄, and tan δ with an increase in tear strength.

The processing aids useful according to the present invention includefatty acid esters of hydrogenated and non-hydrogenated C₅ and C₆ sugarse.g., sorbitose, mannitose and arabinose. These compounds have at leastthree hydroxyl groups and from one to 3.5 ester groups (sesqui esters).Also useful are the polyoxyethylene derivatives thereof. The esterifiedhydrogenated and non-hydrogenated sugars can be described generally bythe following formula using sorbitol as the representative ester

where R is derived from C₁₀ to C₂₂ saturated and unsaturated fattyacids, for example, stearic, lauric, palmitic, oleic and the like.

Representative examples include the sorbitan oleates, includingmonooleate, dioleate, trioleate and sesquioleate, as well as sorbitanesters of laurate, palmate and stearate fatty acids, and polyoxyethylenederivatives thereof, and other polyols and, more particularly, glycols,such as polyhydroxy compounds, and the like. Of these, sorbitan oleatesare preferred, with sorbitan monooleate being most preferred. In similarfashion, other esters can be formed with mannitose and arabinose.Generally, the amount of this processing aid that is employed rangesfrom 0 to about 20 parts by weight, phr, with from about one to about 10phr being preferred. These processing aids are commercially availablefrom ICI Specialty Chemicals under the tradename SPAN, which is aregistered trademark of ICI. Several useful products include SPAN 60(sorbitan stearate); SPAN 80 (sorbitan oleate) and SPAN 85 (sorbitantri-oleate). Other commercially available sorbitans can be used forexample, the sorbitan monooleates known as Alkamuls SMO; Capmul O;Glycomul O; Arlacel 80; Emsorb 2500 and, S-Maz 80. Similar products ofother esters are likewise available.

The polyoxyethylene derivatives of the foregoing processing aidsaccording to the present invention also include fatty acid esters ofhydrogenated and non-hydrogenated C₅ and C₆ sugars e.g., sorbitose,mannitose and arabinose, and have at least three hydroxyl groups andfrom one to 3.5 ester groups (sesqui esters). The polyoxyethylenederived esterified hydrogenated and non-hydrogenated sugars can bedescribed generally by the following formula again, using sorbitol asthe representative ester

where R is derived from C₁₀ to C₂₂ saturated and unsaturated fattyacids, for example, stearic, lauric, palmitic, oleic and the like andthe sum of w+x+y+z equals 20.

The polyoxyethylene derivatives of these processing aids, sometimesreferred to as polysorbates and polyoxyethylene sorbitan esters, areanalogous to the fatty acid esters of hydrogenated and non-hydrogenatedsugars noted above (sorbitans) except that ethylene oxide units areplaced on each of the hydroxyl groups. Representative examples of thepolysorbates include POE (20) sorbitan monooleate; Polysorbate 80; Tween80; Emsorb 6900; Liposorb O-20; T-Maz 80 and the like. The TWEENS arecommercially available from ICI Specialty Chemicals, the tradename TWEENbeing a registered trademark of ICI. Several useful products includeTWEEN 60 [POE (20) sorbitan stearate]; TWEEN 80 [POE (20) sorbitanoleate]; TWEEN 85 [POE (20) sorbitan tri-oleate]; POE (20) sorbitansesquioleate; POE (20) sorbitan laurate; POE (20) sorbitan palmate aswell as TWEEN 20, TWEEN 21, TWEEN 60K, TWEEN 65, TWEEN 65K and TWEEN 81.Generally, the amount of this processing aid that is employed rangesfrom 0 to about 20 parts by weight, phr, with from about one to about 10phr being preferred.

Finally, certain additional fillers can be utilized according to thepresent invention as processing aids which include, but are not limitedto, mineral fillers, such as clay (hydrous aluminum silicate), talc(hydrous magnesium silicate), and mica as well as non-mineral fillerssuch as urea and sodium sulfate. Preferred micas contain principallyalumina, silica and potash, although other variants are also useful, asset forth below. The additional fillers are also optional and can beutilized in the amount of from 0 parts to about 40 parts per 100 partsof polymer (phr), preferably in an amount from about 1 to about 20 phr.

The selection of processing aid(s) and relative amounts for practice ofthe present invention includes the use of any one of the foregoingmaterials, as well as mixtures thereof, as noted hereinabove.Accordingly, various embodiments are possible as follows.

a) The use of fatty acid esters of hydrogenated and non-hydrogenatedsugars alone, in amounts of up to 20 phr. These esters include all ofthe esterified sugars, but not sorbitan monooleate.

b) The use of polyoxyethylene derivatives of the fatty acid esters ofhydrogenated and non-hydrogenated sugars alone, in amounts of up to 20phr.

c) The use of a mineral or non-mineral filler alone or mixtures thereof,in amounts of up to 40 phr. It is to be understood that reference tothese mineral and non-mineral fillers does not include the reinforcingfillers disclosed herein—carbon black and silica.

d) Mixtures of fatty acid esters of hydrogenated and non-hydrogenatedsugars with the polyoxyethylene derivatives thereof, in an amount of upto 20 total phr, with a minimum of at least about one phr of eitherprocessing aid. When such mixtures are utilized, sorbitan monooleate canbe employed.

e) Mixtures of fatty acid esters of hydrogenated and non-hydrogenatedsugars with a mineral or non-mineral filler, as above, in an amount ofup to 30 total phr, with a minimum of at least about one phr of theprocessing aid. When such mixtures are utilized, sorbitan monooleate canbe employed.

f) Mixtures of polyoxyethylene derivatives of the fatty acid esters ofhydrogenated and non-hydrogenated sugars with a mineral or non-mineralfiller, as above, in an amount of up to 30 total phr, with a minimum ofat least about one phr of the processing aid. When such mixtures areutilized, sorbitan monooleate can be employed.

g) Mixtures of fatty acid esters of hydrogenated and non-hydrogenatedsugars with the polyoxyethylene derivatives thereof and with a mineralor non-mineral filler, as above, in an amount of up to 30 total phr,with a minimum of at least about one phr of either processing aid. Whensuch mixtures are utilized, sorbitan monooleate can be employed.

While practice of the present invention includes the addition of atleast one type of processing aid or an additional filler or combinationsthereof, to be effective, preferably at least one part by weight of eachtype that is selected should be employed. Where only a processing aid ormixtures thereof are added, the upper limit is about 20 phr ascontrasted with the use of an additional filler at an upper limit ofabout 40 phr. When a processing aid(s) is present with an additionalfiller, the upper limit total of these additives is about 30 phr.Irrespective of the upper limit amounts stated herein, it is to beappreciated that the combined total filler, that is, reinforcing fillers(silica and carbon black) plus additional fillers (other than silica andcarbon black) will generally not exceed about 25 percent volumefraction. Accordingly, for an elastomeric stock containing additionalfillers at the upper range of about 40 phr, the amount of reinforcingfillers will be lower than where additional fillers have not been added.Unexpectedly, we have found herein that physical properties do not falloff where addtitional filler or fillers are added and the amount ofreinforcing fillers are lowered.

The reinforced rubber compounds can be cured in a conventional mannerwith known vulcanizing agents at about 0.2 to about 5 phr. For example,sulfur or peroxide-based curing systems may be employed. For a generaldisclosure of suitable vulcanizing agents one can refer to Kirk-Othmer,Encyclopedia of Chemical Technology, 3rd ed., Wiley Interscience, N.Y.1982, Vol. 20, pp. 365-468, particularly “Vulcanization Agents andAuxiliary Materials” pp. 390-402. Vulcanizing agents can be used aloneor in combination.

Vulcanizable elastomeric compositions of the invention can be preparedby compounding or mixing the elastomeric polymer with silica, optionallycarbon black, as noted above, and one or more of the processing aids andoptionally additional filler(s) according to the present invention, aswell as other conventional rubber additives including for example,plasticizers, antioxidants, curing agents and the like, using standardrubber mixing equipment and procedures.

GENERAL EXPERIMENTAL

The present invention was demonstrated by comparing tread formulationsas shown in TABLE II in which 3 parts per hundred rubber (phr) Si69(control, C-C) were replaced with 7.5 phr of either an aromatic oil(C-A) or naphthenic oil (C-B). This replacement was further compared toa stock prepared according to the present invention with 3 phr ofsorbitan monooleate and 4.5 phr aromatic oil (Sample 1).

TABLE II Rubber Formulations to Evaluate Silica Modification andPhysical Properties Obtained Materials Amount (parts per hundred rubber)Sample C-A C-B C-C 1 SBR 75 75 75 75 Natural Rubber 25 25 25 25 Silica30 30 30 30 Carbon Black 35 35 35 35 Wax 1 1 1 1 Stearic Acid 1.5 1.51.5 1.5 Zinc Oxide 3 3 3 3 Accelerators 2 2 2 2 Antioxidant 0.95 0.950.95 0.95 Retarder 0.25 0.25 0.25 0.25 Varied Materials Si69 ProcessingAid 0 0 3 0 Sulfur 2.7 2.7 1.7 2.7 Aromatic Oil 7.5 0 0 4.5 NaphthenicOil 15 22.5 15 15 Sorbitan Oleate 0 0 0 3 ML₄ @ 130° C. 72 74 59 59 M50@ 25° C. (psi) 271 295 236 241 M300 @ 25° C. (psi) 1750 1990 1970 1670Tensile @ 25° C. (psi) 2380 2520 2410 2570 % Elongation @ 25° C. 383 361349 419 M200 @ 100° C. (psi) 817 959 921 860 Tensile @ 100° C. (psi)1270 1410 1300 1400 % Elongation @ 100° C. 280 266 256 290 Tear Strength@ 98 95 99 120 171° C. (lb/in) Tan δ @ 50° C. 0.123 0.105 0.132 0.105 Ascan be seen in TABLE II, Sample 1 had better tear strength. The ML₄ @130° C. of Sample 1 has been reduced to the level of the control, C-C,and the 50° C. tan δ is lower than the Samples C-C or C-A and similar tothat of Sample C-B.

A Mooney viscosity reduction of the vulcanizable compound by thesorbitan monooleate (Sor. Oleate) in a high silica containingformulation was also demonstrated with the addition of other ML₄reducing co-agents, summarized in TABLE III hereinbelow.

TABLE III Rubber Formulations to Evaluate Mooney Reduction and TestResults Thereof Material Amount (parts per hundred rubber) SBR 75 PBD 25Silica 80 Carbon Black 8 Modifier Variable (see below) Stearic Acid 1Naphthenic Oil 41.25 Wax 1.5 Resins 1.5 Stabilizers 1.17 Zinc Oxide 1.7Curatives 2.4 Sulfur 2 Cured at 171° C. for 20 minutes Modifier Added(in phr) and ML₄/100° C. Sample Si69 (phr) Modifier 1 phr Modifier 2 phrML₄/100° C. C-D 0   None 0 None  0 161 C-E 8   None 0 None  0 84 2 0.8Sor. Oleate 4 None  0 129 3 0.8 Sor. Oleate 8 None  0 104 C-F 0.8 PEG 4None  0 148 C-G 0.8 PEG 8 None  0 124 C-H 0.8 Sorbitol 4 None  0 146 C-I0.8 Sorbitol 8 None  0 136 4 0   Sor. Oleate 4 OTES  3 73 5 0   Sor.Oleate 4 OTES  2 79 6 0   Sor. Oleate 4 OTES/Talc 3/2 72 7 0   Sor.Oleate 4 OTES/Urea 3/2 70 C-J 0.8 None 0 Mica 15 122 8 0.8 Sor. Oleate 4Mica 15 93 9 0.8 Sor. Oleate 8 Mica 15 77 OTES = Octyltriethoxysilane

As is demonstrated in TABLE III, the sorbitan oleate processing aid wasmore effective in reducing ML₄ at 100° C. than PEG or sorbitol (SamplesC-F to C-I). The addition of a small amount of another silane such asSi69 or OTES gave an even greater ML₄ reduction (Samples 2-5). Co-agentslike urea, talc and mica also had a large effect on ML₄ reduction,especially when used with the sorbitan oleate (Samples 6-9). In fact,there is an effect on ML₄ reduction even when a low level of silane isused along with the sorbitan oleate and mica (compare Samples 8-9 withSample C-J). These results clearly demonstrate the advantage of using aprocessing aid such as sorbitan oleate to reduce ML₄ in silica filledrubber stocks.

We have therefore found that mineral fillers inhibit re-agglomeration ofthe silica in silica-filled vulcanizable elastomer formulations andmaintain the dispersion of the silica, thereby reducing the mixingrequired and aiding in the processability of the compound through adiminished Mooney viscosity. This is demonstrated by the compounding ofthe following formulation to screen silica filled, vulcanizableelastomeric compound properties described below in TABLE IV.

TABLE IV Screening Formulation Material Silica Carbon Black Polymer 100100 Silica 40 Carbon Black 8 45 Si-69 1 Dicyclohexylamine 1 1Antioxidant 1 1 Stearic Acid 2 2 Sulfur 1.4 1.4 Accelerators 2.4 2.4Zinc Oxide 3 3 Totals 159.8 155.8

In this basic formulation, without oil, five parts (by weight) of thesilica were replaced with five parts of either mica, talc, or clay andcompounded with a rubber specifically terminated to interact with fillerthrough residual terminal methylsilylphenoxy groups. The rubber had beenterminated with methyltriphenoxysilane (MeSi(OPh)₃). Both a silica andcarbon black filled stock were used as controls in these examples, asset forth in TABLE V.

TABLE V Partial Silica Replacement with Mineral Fillers Sample C-K 10 1112 C-L Additive Talc Mica Clay Carbon Black Silica 40 35  35  35  CarbonBlack  8 8 8 8 45 Talc 5 Mica 5 Clay 5

The properties of the compounds and the cured stocks are presented inTABLE VI. The uncured compound ML₁₊₄ at 100° C. of the stocks containingtalc and mica were significantly lower than the all silica control.Moreover, the minimum torques (ML) by Monsanto Rheometer were alsolower, indicative of a more processable stock. The hardness and MH ofthe talc and mica stocks indicated a slightly lower state of cure,although only slight differences were shown in the tensile properties.

TABLE VI Physical Test Results Sample C-K 10 11 12 C-L Cpd ML₁₊₄ 100° C.107.8 96.7 97.5 102.7 88.1 Monsanto Rheometer ML 9.55 8.06 8.40 8.786.53 TS₂  3′37″  3′42″  3′46″  3′39″  1′32″ TC₉₀ 12′39″ 10′24″ 10′31″10′42″ 3′17″ MH 43.39 41.27 41.47 42.38 34.60 Shore A 69 65 66 67 67Pendulum Rebound 69.8 71.2 71.8 71.2 63.6 65° C. Ring Tensile 24° C.100% Mod. 598 589 550 558 569 Max. Stress (psi) 2177 2186 2090 1885 2636Max. Strain (%) 298 309 302 289 311 Ring Tensile 100° C. 100% Mod. 473471 443 494 370 Max. Stress (psi) 1002 933 918 948 1712 Max. Strain (%)190 184 188 182 272 Ring Tear 171° C. lb/in 82 68 65 62 95 65° C. Tan δ(@ 7% 0.070 0.063 0.064 0.074 0.121 Elongation) G′, MPa 3.131 3.0043.041 3.163 2.752 ΔG′, MPa 0.586 0.549 0.534 0.655 0.811 Wet Skid 45 4744 43 37

Further testing of silica-filled vulcanizable elastomeric compounds wasconducted to determine the effect of additional mineral fillers and theuse of sorbitan oleate as a processing aid in the stock formulations.These examples are described in TABLES VII, VIII, X and XII, and resultsof the tests reported in TABLES IX, XI, XIII and XIV.

Compound properties displayed in TABLE IX indicated a lower raw compoundML₁₊₄ at 100° C. with lower T80, and lower minimum torque, ML indicativeof an easier processing stock. Tensile properties of the cured stockswere not adversely affected by the mica or talc at these levels andneither was the hardness or state of cure. Further, hot ring tear wasimproved compared to the control. Rebound and Tan δ were indicative oflower rolling resistance stocks.

TABLE VII Basic Formulation (C-M) Parts Masterbatch Material SBR 90.75BR 25 Silica 80 Mica Variable Talc Variable Sorbitan Monooleate VariableSi69, Neat Variable Carbon Black 8 Oil 25.5 Stearic Acid 1 Wax Blend 1.5Resin 3 Final Mixing Material Masterbatch (as above) Processing Aid 0.95Antiozonant 0.22 Zinc Oxide 1.7 Resin 2.5 Accelerators 2.4 SulfurVariable

TABLE VIII Partial Silica Replacement with Talc or Mica Sample C-M 13 1415 16 17 Silica (phr) 80 78.5 76.4 72.7 76.6 73.3 Talc (phr) 0 2 5 10 00 Mica (phr) 0 0 0 0 5 10 Accelerator (phr) 2.4 2.4 2.4 2.4 2.4 2.4Sulfur (phr) 1.6 1.6 1.6 1.6 1.6 1.6 Si69 (phr) 8 8 8 8 8 8

TABLE IX Physical Test Results Partial Replacement of Silica with Talcor Mica Sample C-M 13 14 15 16 17 Mooney Viscometer ML₁₊₄ (100° C.) 82.080.3 77.9 71.0 76.7 71.7 T₈₀ (seconds) 44.3 42.9 34.7 24.5 33.7 26.5Monsanto Cure (170° C.) ML 12.14 12.04 11.46 10.37 11.41 10.47 TS₂ 2′31″  2′30″  2′29″  2′32″  2′37″  2′30″ TC₉₀ 13′52″ 13′08″ 12′11″11′37″ 12′22″ 11′56″ MH 35.38 35.95 35.69 33.97 35.48 34.60 Ring Tensile@ 23° C. 100% Modulus 281 294 335 323 319 315 Max. Stress (psi) 24342449 2601 2709 2634 2510 Max. % Strain 436 430 425 417 436 413 RingTensile @ 100% 100% Modulus 314 258 283 253 274 305 Max. Stress (psi)1580 1405 1447 1264 1471 1485 Max. % Strain 436 430 425 417 436 413 RingTear Strength @ 170° C. 189 239 238 215 256 227 (lb/in) Pendulum Rebound65° C. 50.6 51.6 52.2 54.4 52.6 53.2 Shore “A” Hardness 66.0 70.0 69.065.0 65.0 67.0 Rheometrics @ 65° C. Tan δ @ 7% Strain 0.1871 0.18250.1866 0.1730 0.1694 0.1740 ΔG′, MPa 6.201 7.237 6.825 4.949 6.033 5.498

TABLE X lists variations in order to maintain a constant volume fractionfiller in the basic formulation, provided in TABLE VII. Among thesevariations were included two types of mica to replace some silica andreplacement of Si69 with sorbitan monooleate and silica with a nonreinforcing carbon black, N880. The mica utilized contained 16% Mg andis considered to be the mineral biotite, whereas C-3000 (available fromKMG Minerals Inc, Kings Mountain, N.C.) is muscovite and contains verylittle magnesium. Properties for these formulations are displayed inTABLE XI.

A least squares estimate of the ML₁₊₄ at 100° C. and 0.8 parts Si69 was137 in the all silica formulation. Addition of up to 15 parts micacaused a significant decrease in the observed value which was enhancedby the addition of sorbitan monooleate. There was an unexpectedsynergism of these additives on reduction of ML₁₊₄, t80, and ML. MH,tensile, and hardness, all indicative of a lower state of cure, werereduced by the sorbitan monooleate. These effects were also reflected inthe tensile retraction data as well.

Adjustment of curatives compensated for the lower cure rate. Even at thelower state of cure, these stocks had lower Tan δ values indicative oflower rolling resistance and increased fuel efficiency. This was furtherenhanced with a tighter cure.

TABLE X Partial Silica Replacement with Mica Sample C-N C-O C-P C-Q C-RC-S 18 19 20 21 22 23 C-T C-U 24 Silica (phr) 80 80 80 80 80 80 80 8072.8 69.2 69.2 69.2 73.3 73.3 69.2 Mica (phr) 0 0 0 0 0 0 0 0 10 15 1515 0 0 15 Mica Type — — — — — — — — B B B M — — M N880 (phr) 0 0 0 0 0 00 0 0 0 0 0 0 6.21 0 Sorbitan 0 0 0 0 0 0 4 8 0 0 4 8 0 0 0 MonooleateAccelerator 1 1.6 1.9 2.2 2.5 2.2 2.2 2.2 2.2 2.2 2.2 2.5 2.2 1.6 1.62.2 (phr) Sulfur (phr) 1.6 1.5 1.4 1.3 1.6 1.2 1.8 1.8 1.8 1.8 1.7 1.91.6 1.6 1.8 Si69 (phr) 8 8 8 8 4 12 0.8 0.8 0.8 0.8 0.8 0 8 8 0.8Accelerator 2 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.80.8 (phr) B = BIOTITE M = MUSCOVITE

TABLE XI Physical Test Results Partial Replacement of Silica with MicaSample C-N C-O C-P C-Q C-R C-S 18 Mooney Viscometer ML₁₊₄ @ 100° C. 82.978.4 79.8 81.3 119.7 68.1 129.1 T₈₀ 38.8 31.3 34.7 35 1154 17 730Monsanto Cure @ 170° C. ML 12.81 12.46 12.08 12.46 19.82 10.03 24.59 TS₂ 2′29″  2′29″ 2′34″ 2′31″  2′07″  2′18″  2′17″ TC₉₀ 13′16″ 11′36″ 9′29″7′37″ 17′43″ 11′03″ 17′52″ MH 36.91 36.71 35.45 36.68 42.95 38.12 44.36Ring Tensile @ 23° C. 100% Modulus 362 327 343 351 294 390 236 Max.Stress (psi) 2793 2537 2798 2760 2479 2521 2216 Max. % Strain 511 504525 518 557 457 729 Ring Tensile @ 100° C. 100% Modulus 353 293 285 326294 355 183 Max. Stress (psi) 1555 1464 1418 1538 1470 1386 1444 Max. %Strain 363 394 386 379 411 333 739 Ring Tear @ 170° C. 245 257 243 237233 280 176 Strength (lb/in) Pendulum Rebound 51.8 51.8 52.0 52.8 52.254.8 49.0 65° C. Shore “A” Hardness 72.0 69.0 70.0 70.0 72.0 70.0 68.0Rheometric @ 65° C. Tan δ @ 7% Strain 0.1815 0.1834 0.1904 0.19 .017070.1751 0.1837 ΔG′, MPa 8.329 8.247 8.754 9.227 9.267 7.488 9.762 TensileRetraction M₀ (×10⁻⁴), g/mol 1.23 1.15 1.25 1.14 1.26 1.05 1.43 Slope(×10⁻³), g/mol 3.06 3.07 3.16 3.09 3.73 2.86 4.95 β (×10⁻³), g/mol 5.705.91 5.99 5.11 4.06 5.55 3.90 Sample 19 20 21 22 23 C-T C-U 24 MooneyViscometer ML₁₊₄ @ 100° C. 103.5 135.7 122.0 92.7 76.6 69.8 73.6 123.6T₈₀ 300 1510 592 109.5 27.2 18.7 21.4 1316.6 Monsanto Cure @ 170° C. ML19.28 26.83 23.03 16.46 13.63 10.03 10.37 22.59 TS₂  2′39″  1′53″  1′57″ 2′30″  3′13″  2′27″  2′20″  1′49″ TC₉₀ 15′24″ 18′45″ 18′24″ 13′16″12′10″ 12′06″ 10′49″ 18′45″ MH 39.24 47.72 44.36 37.25 31.80 33.35 34.5743.14 Ring Tensile @ 23° C. 100 % Modulus 191 273 258 205 166 237 265271 Max. Stress (psi) 1916 2389 2281 2123 1559 2551 2796 2283 Max. %Strain 768 665 675 782 831 616 618 678 Ring Tensile @ 100° C. 100%Modulus 151 208 231 176 134 268 287 280 Max. Stress (psi) 1296 1311 14021399 959 1392 1381 1242 Max. % Strain 821 585 584 745 826 433 414 530Ring Tear @ 278 272 247 267 212 260 246 237 170° C. Strength (lb/in)Pendulum Rebound 46.8 51.8 53.0 51.4 47.6 53 52.8 51.6 65° C. Shore “A”Hardness 66.0 75.0 70.0 65.0 62.0 67.0 69.0 75.0 Rheometric @ 65° C. Tanδ @ 7% Strain 0.1935 0.1791 0.1798 0.1819 0.1932 0.1851 0.1792 0.1701ΔG′, MPa 8.351 9.676 8.826 7.022 5.185 5.749 5.656 10.165 TensileRetraction M₀ (×10⁻⁴), g/mol 1.6 1.26 1.29 1.59 1.87 1.10 1.10 1.26Slope (×10⁻³), 5.63 4.69 5.12 5.53 7.03 2.93 2.98 4.94 g/mol β (×10⁻³),g/mol 4.07 3.42 4.35 5.61 7.95 6.35 6.72 4.02

TABLE XII describes additional variations in formulation as well asincluding other types of mica. The particular mica was unimportant inthe ML4 reduction which ranged from about 12 to 14 points at 15 partsmica per 100 rubber, shown in TABLE XIII. Nor, were there significanteffects of mica type on ML or T₈₀ reductions. The mica stocks showedhigher rebound and reduced tan δ values at comparable states of cure asjudged from tensile properties. Hardness values indicated a lower stateof cure for the mica stocks however, a change of filler type may notallow direct comparison of hardness to judge state of cure.

TABLE XII Partial Silica Replacement with Mica Change of Cure SystemSample C-V C-W C-X C-Y 25 26 27 28 29 C-Z Recipe Per C-P C-P C-P C-P C-PC-P C-P C-P C-P C-P Previous Stock ZnO (phr) 1.70 2.40 3.00 3.00 1.701.70 1.70 3.00 3.00 1.70 Stearic Acid 1.00 1.00 1.00 2.00 1.00 1.00 1.001.00 1.00 1.00 (phr) Silica (phr) 80 80 80 80 69.2 69.2 69.2 69.2 69.280 Mica Muscovite 0 0 0 0 15 0 0 0 0 0 (phr) Water Ground 0 0 0 0 0 15 00 0 0 325 Mesh Mica Muscovite (phr) C3000-SM-M 0 0 0 0 0 0 15 15 15 0(phr) Silane Treated Si69/CB 16 16 16 16 16 16 16 16  0(*) 16 Mixture(1:1) (phr) Sulfur (phr) 1.40 1.40 1.40 1.40 2.20 2.20 2.20 2.20 2.202.20 (*)Add 8.0 phr N330 Carbon Black to Compensate for that in 16.00phr

TABLE XIII Physical Test Results Effect of Presence of Mica, Type ofMica and of Cure System Variations at Constant Mixing Energy Input(238.4 w-hrs/lb) Sample C-V C-W C-X C-Y 25 26 27 28 29 C-Z MooneyViscometer ML₁₊₄ 100° C. 75.7 73.4 74.5 71.5 58.7 60.1 60.4 60.2 125.172.7 T₈₀ 24.1 22.7 24.1 22.4 19.7 15.9 15.6 14.6 >300.6 26.1 MonsantoCure (170° C.) ML 11.6 11.17 11.36 10.59 8.94 8.85 9.38 8.60 25.86 10.97TS₂  2′30″ 2′31″  2′36″ 2′42″  2′19″  2′21″  2′18″  2′27″  2′11″  2′12″TC₉₀ 10′01″ 9′43″ 10′11″ 8′49″ 11′01″ 10′49″ 11′07″ 11′53″ 20′49″ 12′55″MH 37.37 37.08 37.70 35.43 39.44 39.16 40.70 38.43 48.24 41.52 RingTensile @ 23° C. 100% Modulus 318 333 327 301 393 430 387 368 256 368MAX. Stress (psi) 2809 3107 2927 2819 2604 2766 2681 2452 1886 2714Energy To Break (psi) 6596 7435 7132 7038 5540 5977 5989 5212 5293 5399Ring Tensile @ 100° C. 100% Modulus 268 276 281 248 321 347 366 341 220366 Max. Stress (psi) 1263 1631 1503 1483 1093 1255 1376 1436 1212 1811Max. % Strain 364 439 417 451 324 334 341 368 671 361 Ring Tear @ 170°C. 276 307 305 322 253 253 261 246 240 253 Tear Strength (lb/in)Pendulum Rebound 53.6(*) 53.0(*) 54.8 53.6 59.6 58.8 58.8 58.6 51.2 55.865° C. Shore “A” Hardness 65.0 67.0 67.0 68.0 68.0 68.0 67.0 68.0 72.070.0 Rheometrics @ 65° C. Tan δ @ 7% Strain 0.1839 0.1868 0.1764 0.18550.1436 0.1458 0.1471 0.1480 0.1679 0.1875 ΔG′, MPa 6.881 6.167 5.9505.290 4.745 5.146 5.063 4.792 10.08 5.831 (*)Samples not well molded

TABLE XIV lists the results of controlled mix studies into which a knownenergy input was applied to a mix after the Si69 was added in thepresence of mica, talc, and/or sorbitan monooleate. It has beenestablished that β, an inverse measure of filler association orcrosslink density, as determined by tensile retraction, can be increasedby more mixing energy. This effect can be calculated from the slope of33.99 g/mol mix energy, and intercept, 1349 g/mol, (see drawing figure)and applied to the mix energy supplied to the samples.

The data in TABLE XIV have been sorted by increasing Si69, Mica, andTalc in that order. The Δβ value, the increase in β over that expected,increased with Si69 and the Mica and Talc level and have thusly beengrouped. The two exceptions were the combination of Mica (15 parts) withsorbitan monooleate (8 parts) and the sorbitan monooleate alone (8parts) which showed much higher β than expected from mix energycalculations alone.

TABLE XIV Tensile Retraction of Controlled Energy Mixes Energy AfterSi69 was Added to a 280 g Brabender Mr S β Energy Si69 Sulfur Sampleg/mol g/mol S/Mr g/mol W/H phr phr 23 16700 7034 0.421 7947 112.17 0 1.920 109.13 4910 0.450 2057 72.73 0.8 2 18 14270 4945 0.347 3899 106.130.8 1.8 30 16040 5626 0.351 4069 103.83 0.8 1.8 19 11387 2686 0.236 581175.40 0.8 2 20 12630 4690 0.371 3415 101.44 0.8 1.8 31 12640 4944 0.3914022 104.93 0.8 1.8 24 12930 5122 0.396 4354 113.16 0.8 1.8 22 158755532 0.348 5615 123.10 0.8 1.7 17 10475 2547 0.243 5697 147.00 8 2.2 2512184 3247 0.268 6668 147.00 8 1.4 C-V 10980 2928 0.267 6346 117.05 81.6 C-U 12304 3061 0.249 5702 93.51 8 1.6 28 12890 3010 0.234 5579 80.378 1.8 C-T 11040 2980 0.270 6716 109.72 8 1.6 C-M 12656 3130 0.247 605887.65 8 1.6 13 12398 3352 0.270 6835 88.70 8 1.6 14 12690 3443 0.2717380 96.59 8 1.6 15 12491 3270 0.262 6706 89.88 8 1.6 16 12579 34230.272 7880 92.61 8 1.6 32 9111 3098 0.340 8289 147.00 8 2.2 C-Z 92993082 0.331 8309 147.00 8 2.2 26 9348 3155 0.338 8630 147.00 8 2.2 279849 3141 0.319 8708 147.00 8 2.2 ACC MICA TALC SO CALC β Δβ Sample phrphr phr phr g/mol g/mol 23 3.0 15  0 8 5161 2786 20 2.4 0 0 0 3820 −176318 3.0 0 0 4 4956 −1057 30 3.0 0 0 8 4878 −809 19 2.4 0 0 8 3912 1899 203.0 10  0 0 4796 −1381 31 3.0 15  0 0 4915 −893 24 3.0 15  0 0 5195 −84122 3.0 15  0 4 5533 82 17 2.4 0 0 0 6345 −648 25 3.0 0 0 0 6345 323 C-V2.4 0 0 0 5327 1019 C-U 2.4 0 0 0 4527 1175 28 3.0 0 0 0 4080 1499 C-T2.4 0 0 0 5078 1638 C-M 2.4 0 2 0 4328 1730 13 2.4 0 5 0 4363 2472 142.4 0 10  0 4632 2748 15 2.4 5 0 0 4403 2303 16 2.4 10  0 0 4496 3384 322.4 15  0 0 6345 1944 C-Z 2.4 15  0 0 6345 1964 26 2.4 15  0 0 6345 228527 2.4 15  0 0 6345 2363

It is therefore unexpected that mica and talc should decrease the fillerinteraction and increase β as their levels were increased. Further,sorbitan monooleate, alone and in concert with mica, acted to increasethe observed β and thus reduce filler interaction.

Further testing of silica-filled vulcanizable elastomeric compounds wasconducted to determine the effect of mineral fillers and the use ofpolyoxyethylene derivatives of fatty acid esters of hydrogenated andnon-hydrogenated sugars as processing aids in the stock formulations.These examples are described in TABLE XV with the results of the testsconducted to evaluate and compare physical properties. As a Control,Sample C-C was prepared as above, without any fatty acid esteradditives. The ethoxylated species (Tweens) are presented as Samples 30,32, 33 and 37 and are compared against analogous sorbitans (Spans,non-ethoxylated), Samples 31, 34, 35 and 36. The Samples containedcarbon black 35 phr, 30 phr of silica and 3 parts by weight of Si69 (10percent per weight of silica) and were prepared with the formulation asset forth in Table II, Sample C-C, to which the processings aids ofTable XV were added. The processing aids included Spans (fatty acidesters) and Tweens (polyoxyethylene fatty acid esters).

TABLE XV Physical Test Results Effect of Partial Replacement of Silicawith Sorbitan Esters Sample C-C 30 31 32 33 34 35 36 37 Additive — Tween80 Span 80 Tween 60 Tween 85 Span 60 Span 85 Span 80 Tween 80 Level, phr— 3 3 3 3 3 3 1.5 1.5 Mooney Viscosity ML₁₊₄ 100° C. 60.3 52 50.2 53.850.5 49.5 52.3 53.5 56.7 T₈₀ 7.8 6.7 6.7 6.7 5.3 5.4 5.7 5.7 6 MonsantoCure (165° C.) ML* 2.56 2.34 1.87 2.43 7.25 8.52 7.25 7.44 8.17 TS₂2′58″  3′27″  3′30″  3′33″  4′47″  4′41″  4′27″  4′22″  4′38″ TC₉₀ 9′43″11′46′ 11′29″ 11′56″ 14′38″ 13′34″ 12′16″ 12′25″ 11′56″ MH* 15.69 16.4214.68 17.94 40.36 37.88 37.88 38.55 41.67 Ring Tensile @ 24° C. 100%Modulus 465 485 600 472 363 446 393 383 394 Max. Stress (psi) 2278 22643595 2218 3274 2956 2961 2706 2466 Energy To Break (in- 3374 3398 63803384 4169 5403 5705 4965 4319 lbs/in³) Ring Tensile @ 100° C. 100%Modulus 371 387 379 375 329 298 315 338 346 Max. Stress (psi) 1228 12551268 1272 1492 1216 1417 1437 1389 Max. % Strain 257 251 260 263 311 288313 304 286 Ring Tear @ 171° C — — — — 112 148 123 124 118 Tear Strength(lb/in) Pendulum Rebound 51.4 53 52 53 50.2 50 51.8 50.6 50.8 65° C.Rheometrics Tan δ @ 7% Strain 0.1389 0.1207 0.1232 0.1088 0.1155 0.12140.1209 0.1319 0.1266 ΔG′, MPa at 65° C. 2.752 2.922 2.243 2.551 2.4172.475 2.144 2.45 2.697 *ML and MH values for Samples C-C and 30-32 weremeasured on a Monsanto MDR 2000 rheometer and ML and MH values forSamples 33-37 were measured on a Monsanto ODR rheometer.

As is apparent from the physical properties reported in Table XV, theethoxylated sorbitans (Tweens) provided improved properties over theControl and generally performed as well as the sorbitans (Spans). Allaids were fairly well equivalent, showing reduced Mooney viscosity andtorque while desired physical properties remained. Unexpectedly, theneed for adjacent hydroxyls in the sorbitan molecule, as taught byCanadian Pat. No. 2,184,932 to Semerit, was found to be unfounded as theuse tri-oleates, which contain only a single hydroxyl, were effective inproducing processability as was equally true for the polysorbates whichare polyethoxylated and thus, contain no adjacent hydroxyls.

Thus, it should be evident that the process of the present invention isuseful in improving the processability of formulations of diene polymerelastomers containing silica filler by reducing the viscosity ofsilica-filled elastomeric vulcanizable compounds. It is furtherdemonstrated that the present invention provides vulcanizablesilica-filled elastomeric compounds having enhanced physical properties.Practice of the present invention allows a reduction of silanes whichare added to vulcanizable rubber compositions containing silica fillers.The reduction can be effected by the addition of the processing aidsdescribed herein, mineral and non-mineral fillers as well ascombinations of more than one.

It will be appreciated that the processing aids and additional fillersexemplified herein have been provided to demonstrate practice of theinvention and are otherwise not to be construed as a limitation onpractice of the present invention. Moreover, the processing aids andmineral fillers disclosed herein have been provided for purposes ofexemplification only and thus, it is to be appreciated that othermaterials can be substituted without falling outside of the scope ofthis invention. Those skilled in the art can readily determine suitableadditives and the appropriate manner of formulating elastomericcompositions containing silica fillers. Furthermore, practice of thepresent invention is not limited to a specific formulation ofelastomers.

Based upon the foregoing disclosure, it should now be apparent that theprocess and related components described herein will carry out theobjects set forth hereinabove. It is, therefore, to be understood thatany variations evident fall within the scope of the claimed inventionand thus, the selection of specific component elements can be determinedwithout departing from the spirit of the invention herein disclosed anddescribed. Thus, the scope of the invention shall include allmodifications and variations that may fall within the scope of theattached claims.

We claim:
 1. A sulfur vulcanizable elastomeric compound having a reducedviscosity prior to vulcanization, comprising: 100 parts by weight of anelastomer optionally comprising a terminal alkoxysilane functional groupand selected from the group consisting of homopolymers derived fromconjugated diene monomers and copolymers comprising monomer unitsderived from a conjugated diene monomer and a monomer unit selected fromthe group consisting of monovinyl aromatic monomers and triene monomers;about 5 to about 100 parts by weight of a reinforcing filler per 100parts of elastomer, wherein the reinforcing filler is selected from thegroup consisting of silica filler and mixtures thereof with carbonblack; zero to about 20 percent by weight of a silane, based upon theweight of said silica filler; sulfur; a processing aid selected from thegroup consisting of (i) about one to about 20 parts by weight of a fattyacid ester of a hydrogenated or non-hydrogenated C₅ or C₆ sugar, (ii)about one to about 20 parts by weight of a polyoxyethylene derivative ofa fatty acid ester of a hydrogenated or non-hydrogenated C₅ or C₆ sugar,and (iii) mixtures of selections from (i) and (ii); and about one toabout 40 parts by weight of an additional filler selected from the groupconsisting of mica, urea, sodium sulfate, and mixtures thereof, whereinthe presence of both the processing aid and the additional fillerreduces the viscosity of the compound prior to vulcanization compared toa compound comprising the processing aid alone.
 2. The compound as setforth in claim 1 wherein the elastomer is styrene-butadiene rubber. 3.The compound as set forth in claim 1, further containing a naturalrubber.
 4. The compound as set forth in claim 1, wherein the silicafiller has a surface area of about 32 to about 400 m²/g.
 5. The compoundas set forth in claim 1, wherein the silica filler has a pH of about 5.5to about
 7. 6. The compound as set forth in claim 1, wherein the amountof said carbon black ranges from 0 to about 50 parts by weight, per 100parts by weight of elastomer, and the amount of said reinforcing silicafiller ranges from about 1 to about 100 parts, per 100 parts ofelastomer, with the proviso that where carbon black is 0, at least 30phr of silica is employed.
 7. The compound as set forth in claim 1,wherein said fatty acid ester of a hydrogenated or non-hydrogenated C₅or C₆ sugar is selected from the group consisting of sorbitanmonooleate, sorbitan dioleate, sorbitan trioleate, sorbitansesquioleate, sorbitan laurate, sorbitan palmitate and sorbitanstearate.
 8. The compound as set forth in claim 1, wherein saidpolyoxyethylene derivative of a fatty acid ester of a hydrogenated ornon-hydrogenated C₅ or C₆ sugar is selected from the group consisting ofPOE (20) sorbitan stearate; POE (20) sorbitan oleate; POE (20) sorbitantrioleate; POE (20) sorbitan sesquioleate; POE (20) sorbitan laurate andPOE (20) sorbitan palmitate.
 9. The composition as set forth in claim 1,wherein the silane is selected from the group consisting ofbis[3-(triethyoxysilyl)-propyl]tetrasulfide, n-octyl triethoxysilane,and mixtures thereof.